Heat-shrinkable film

ABSTRACT

Disclosed is a cross-linked heat shrinkable film comprising an ethylene polymer resin which has a gel fraction of 5-40%. Furthermore, this film contains a glycerin fatty acid ester surface active agent in an amount of 2.0-8.0% by weight based on the total weight of the ethylene polymer resin, said surface active agent being present in an amount of 3.0-20.0 mg/m 2  on at least one surface of the film. This film has characteristics adaptable to speeding-up of continuous packaging machines, namely, a proper coefficient of dynamic friction and hot tack sealability, with maintaining appearance of the film after being shrunk, such as heat shrink characteristics, fog resistance and gloss.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/09519 which has an Internationalfiling date of Oct. 30, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a heat shrinkable film which can givegood appearance packages by heat shrinking. Particularly, it relates toa heat shrinkable film excellent in balance in fog resistance, opticalcharacteristics and physical properties for adaptability to packagingmachines and, additionally, sealability on high-speed packagingmachines.

BACKGROUND ART

Methods of packaging with films include, for example, household wrappackaging, twist packaging, sack packaging, skin packaging, shrinkpackaging, stretch packaging, and the like. Among them, since the shrinkpackaging can package tightly the articles to be packaged and canenhance the commercial value of packages, this method is suitably usedfor packaging of foods, miscellaneous goods, etc. Heat shrinkable filmsused for the shrink packaging are required to have the followingcharacteristics: (1) they can tightly finish the package without causingdeformation of the articles to be packaged; (2) they are low in haze andhigh in gloss, and can finish the package with beautiful appearance ofcontents; (3) they are not hazed with water droplets in refrigerationand are superior in visibility of the contents; and others.

In addition, for continuous shrink packaging of a plurality of articles,in general, the articles are primarily packaged by pillow packaging oroverlap packaging with leaving some allowance between the film and thearticle, and then the packaged articles are passed through a heat shrinktunnel to heat shrink the film.

Recently, packaging by continuous packaging machines has been speededup, and hence, the characteristic required for heat shrinkable filmsused for the packaging have become severer. Main characteristicsrequired for heat shrinkable films used on continuous packaging machinesare as follows:

-   -   (4) With speeding-up of continuous packaging machines, the films        must be superior in slipperiness between the machines and the        films.    -   (5) They must have hot tack sealing strength to perform firm        sealing in a short time.

As heat shrinkable films, there are known multi-layer films comprisingvarious ethylene polymers. For example, JP-A-5-131599 discloses apolyethylene heat shrinkable laminate film excellent in adaptability topackaging machines which contains in inner, outer and intermediatelayers a linear low density polyethylene specified in density and meltindex.

Furthermore, JP-A-5-105787 discloses a resin composition for films whichcomprises a mixed resin of a linear low density polyethylene and a lowdensity ethylene-α-olefin copolymer specified in melt index to which aspecific amount of an anti-fogging agent is added.

On the other hand, JP-A-6-106668 discloses a cross-linked filmcomprising an ethylene polymer resin having proper heat shrinkage, heatshrinkage stress and tear strength and excellent in transparency.

However, these films have the following problems.

The film disclosed in JP-A-5-131599 is excellent in sealability, butinferior in heat resistance, and the temperature of heat shrink tunnelor heat sealing temperature cannot be high. For these reasons, the filmhas a restriction in packaging conditions for performing high-speedpackaging.

AS for the film disclosed in JP-A-5-105787, enhancement of fogresistance is aimed at by improving bleeding-out of surface activeagent, but no sufficient fog resistance has been obtained. Moreover,since this film is cross-linked, raising of heat sealing temperature isapt to cause failure in sealing due to fusion bonding of the film to asealing bar or extension of sealed portions. Therefore, this film cannotbe applied to high-speed continuous packaging machines.

The film disclosed in JP-A-6-106668 is a cross-linked and stretchedfilm, and hence, is improved in heat resistance and has proper heatshrinkage and heat shrinkage stress, and further is good in sealability.However, since the film is insufficient in slipperiness, it is apt to bebroken when the continuous packaging machine is operated at high speed.In addition, the film is insufficient in fog resistance.

The object of the present invention is to provide a heat shrinkable filmwhich satisfies characteristics to be adapted for speeding-up ofcontinuous packaging machines, namely, proper coefficient of dynamicfriction and hot tack sealability with keeping heat shrinkcharacteristics and appearance after shrinking, such as fog resistanceand gloss.

DISCLOSURE OF INVENTION

As a result of intensive research conducted by the inventors in anattempt to attain the above object, the present invention has beenaccomplished.

That is, the present invention is a cross-linked heat shrinkable filmcomprising an ethylene polymer resin where the film has a gel fractionof 5-40% and contains a glycerin fatty acid ester surface active agentin an amount of 2.0-8.0% by weight based on the total weight of theethylene polymer resin, said surface active agent being present in anamount of 3.0-20.0 mg/m² on at least one surface of the film.

Furthermore, a method for producing the heat shrinkable film of thepresent invention includes the steps of kneading an ethylene polymerresin and a glycerin fatty acid ester surface active agent using anextruder, molding an unstretched tube, cross-linking the resultingunstretched tube, and stretching the tube, wherein at least a part ofthe kneading step is carried out at a temperature of 250° C. or higherand at a shear rate of 50 [1/sec] or higher.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained in detail below.

First, the heat shrinkable film of the present invention is across-linked film comprising an ethylene polymer resin.

As the ethylene polymer resin, mention may be made of resins comprisingcopolymers of ethylene and α-olefins, such as high density polyethylene,intermediate density polyethylene, low density polyethylene, linear lowdensity polyethylene and ultra-low density polyethylene; resinscomprising copolymers of ethylene and vinyl compounds copolymerizablewith ethylene, such as ethylene-vinyl acetate copolymer, and the like.

Of these ethylene polymer resins, linear low density polyethylene andultra-low density polyethylene which are produced by polymerizationusing Ziegler multi-site catalysts or single-site catalysts such asmetallocene catalysts are preferred because they are excellent inuniformity of cross-linking, stretching stability, transparency,slipperiness, and sealability.

Moreover, when amount of a low-molecular weight component, namely, acomponent of not more than 10,000 in molecular weight, is 10% by weightor less in the ethylene polymer resins, ethylene chains which containless short chains are obtained. Therefore, cross-linking degree can bereadily adjusted and slipperiness and hot tack sealability after moldinginto films are improved. These resins can be obtained by usingsingle-site catalysts (hereinafter, these resins being sometimesreferred to as “single-site resins” or “SSC resins”). Examples of theseresins are “Evolue” (trademark) manufactured by Mitsui Chemical Co.,Ltd., “UMERIT” manufactured by Ube Industries, Ltd., “Elite” (trademark)manufactured by Dow Chemical Co., Ltd., and the like.

Furthermore, in the present invention, it is more preferred to use, asthe ethylene polymer resin, a linear low density polyethylene orultra-low density polyethylene in which α-olefin is hexene-1 oroctene-1.

Density [ρ] of the ethylene polymer resins is preferably 0.900-0.934g/cm³. When the density is within this range, a proper stiffness isgiven to the film, and film thickness can be made thin, and, besides,more transparent film can be obtained. The density of the ethylenepolymer resins is more preferably 0.910-0.927 g/cm³.

In order to obtain good optical characteristics even for such films asstretched at high ratios and at high temperatures, MI of the ethylenepolymer resins is preferably 0.5-5.0, more preferably 0.8-4.0.

The heat shrinkable film of the present invention is preferably alaminate film comprising at least 3 layers composed of outer layers andan inner layer.

The ethylene polymer resin used for the outer layers is preferably anethylene copolymer resin, and from the points of hot tack sealabilityand optical characteristics, the density of the resin is preferably0.904-0.927 g/cm³, more preferably 0.910-0.918 g/cm³. It is especiallypreferred to use an ethylene-α-olefin copolymer, a low densitypolyethylene or mixtures thereof as the ethylene copolymer.

Particularly, when a mixed resin of an ethylene-α-olefin copolymer and alow density polyethylene is used, fine crystals are dispersed in theresin and hence, a film layer in which the surface active agentuniformly bleeds out can be obtained. Moreover, the mixed resin is alsopreferred because of diminishment in generation of foreign matters whichis apt to occur when the ethylene-α-olefin copolymer resin is stirredunder the conditions of high temperature and high speed. In the case ofusing a low density polyethylene as the ethylene copolymer resin, theamount thereof is preferably 4-30% by weight based on the weight ofresin in the total outer layers. Furthermore, when an ethylene-α-olefincopolymer obtained using a single-site catalyst (SSC resin) is used, theslipperiness is very good and hence, use of this ethylene-α-olefincopolymer is especially preferred.

The ethylene polymer resin used for the inner layer preferably has adensity of 0.913-0.927 g/cm³, because this resin is high in efficiencyof cross-linking with electronic rays and high in melt tension at thetime of heating, and hence, is highly improved in stability atstretching. It is particularly preferred to use an ethylene-α-olefincopolymer resin or a mixture of an ethylene-α-olefin copolymer and a lowdensity polyethylene. When the ethylene-α-olefin copolymer is oneobtained using a single-site catalyst, the copolymer has a structure ofmany molecular chains being present in a main chain and, therefore, ishigh in film-forming stability. Further, from the point of stretchingstability, it is preferred to use a mixed resin of a linear low densitypolyethylene and a low density polyethylene as the ethylene polymerresin. In the case of using a low density polyethylene as the ethylenepolymer resin, amount of the low density polyethylene is preferably4-30% by weight based on the weight of the resin in the total innerlayer.

The above ethylene polymer resin may contain a small amount of a lowdensity polyethylene or a comonomer as an auxiliary component.

As mentioned above, the heat shrinkable film of the present inventioncomprises a cross-linked ethylene polymer resin. When a properlycross-linked ethylene polymer resin is made to a heat shrinkable film, astable stretching can be performed even at a temperature higher than themelting point of the resin, control of stretching temperature andstretching ratio becomes easy, and thus a heat shrinkable film having alow heat shrinkage stress is obtained with keeping a high heatshrinkage.

Specifically, it is necessary to cross-link the ethylene polymer resinso that the gel fraction of the film which is an indication forcross-linking degree is in the range of 5-40%. If the gel fraction ofthe film is less than 5%, it sometimes becomes difficult to stably formthe film at the time of stretching at high temperatures. If it exceeds40%, the heat shrinkage stress becomes too high, and soft articles to bepackaged are sometimes deformed. When the gel fraction of the film iswithin the above range, in addition to the above-mentioned points, hazeof the heat shrinkable film after being shrunk can be improved, andfurthermore when the film is shrunk by heating at a temperature higherthan the melting point of the resin which constitutes the film, the filmcan be prevented from melting and breaking.

In the present invention, the gel fraction of the film is morepreferably 10-40%. The gel fraction is especially preferably 15-35%,because stretching is stabilized and a suitable heat shrinkage stresscan be obtained.

The film is cross-linked by irradiating the film with ionizing radiationsuch as α-rays, β-rays, γ-rays, neutron rays, electron rays, and thelike. Degree of irradiation is preferably 2-10 megarads. Within thisrange, degree of the haze of the film after subjected to heat shrinkingis proper while the heat shrinkage stress of the film is low, and thus,beautiful shrink packaged articles can be provided. If irradiation ofhigher than 10 megarads is carried out, heat shrinkage stress of thefilm becomes too large upon stretching, and as a result the film breaksat the portions of small holes provided for removal of air, the sealedportions are peeled, or the articles to be packaged are deformed, andhence, beautiful shrink packaged articles cannot sometimes be obtained.

Considering also the conditions under which mechanical unevenness suchas in thickness and flow speed of the film does not occur, the degree ofirradiation is more preferably 4-8 megarads. Since the relation betweenthe degree of irradiation and the resulting gel fraction differsdepending on the kind of resin, the irradiation dose is set depending onthe resin used.

Next, a glycerin fatty acid ester surface active agent is present in oron the surface of the heat shrinkable film of the present invention.

The glycerin fatty acid ester surface active agent (which may behereinafter referred to as merely “surface active agent”) is an ester ofa polyhydric alcohol and a fatty acid, and hydrophilicity andoleophilicity thereof can be controlled by changing polymerizationdegree of glycerin, kind of the fatty acid or esterfication degree. Byallowing the surface active agent to be present on the surface of thefilm, fog resistance can be given to the film. More preferred surfaceactive agents are those which are mainly composed of diglycerin oleate,diglycerin laurate, glycerin monooleate or mixtures thereof because theyhardly damage slipperiness and optical characteristics of the film. Itis especially preferred to use a mixture consisting of diglycerin oleateand glycerin monooleate at 1:1 as the surface active agent.

The characteristics of the heat shrinkable film of the present inventionvary depending on the kind of the ethylene polymer resin, the amount ofthe surface active agent, the kind of the surface active agent, and theblending ratio of the surface active agent and the ethylene polymerresin. Therefore, a heat shrinkable film capable of attaining the morepreferable effects can be obtained by selecting a specific ethylenepolymer resin and a specific surface active agent, and adjusting theamount of the surface active agent and the blending ratio of the surfaceactive agent and the ethylene polymer resin to specific ranges. As oneexample of the most preferred embodiments in the present invention,mention may be made of a film of three layers comprising a laminate ofouter layers and inner layer as shown below.

The outer layers comprise a mixture of an ethylene-hexene-1 copolymer(70-96% by weight) obtained using a single-site catalyst and a lowdensity polyethylene (4-30% by weight), and both the outer layerscontain a surface active agent mainly composed of diglycerin oleate andglycerin monooleate.

The inner layer comprises a mixture of ethylene-octene-1 copolymer(70-96% by weight) obtained using a multi-site catalyst and a lowdensity polyethylene (4-30% by weight), or a mixture of a resin (70-96%by weight) mainly composed of an ethylene-hexene-1 copolymer obtainedusing a single-site catalyst and a low density polyethylene (4-30% byweight).

The conventional techniques according to which the surface active agentis only coated on the surface of the film have the problems that thefilm is poor in retention of fog resistance and, further, the amount ofthe surface active agent present on the surface of the film (hereinafterreferred to as “amount on film surface” is difficult to control. On theother hand, according to the present invention, these problems aresolved by allowing the surface active agent to bleed out at a highconcentration on the surface of the film.

Moreover, it is preferred that the surface active agent is present onthe surface of the film not in the state of droplets, but in the stateof a band, namely, in nearly continuous state. That the surface activeagent is present in the state of a band means that the surface activeagent is present on the surface of the film without causing exposure ofthe film substrate and, besides, is also present in the portion of thefilm which is in the vicinity of the surface in the continuous state, inother words, is present in continuous state both inside and outside thefilm with the surface of the film constituting an interface between theoutside and the inside. The surface active agent band may notnecessarily be present with uniform thickness and thickness of thesurface active agent band may have unevenness in conformity to theirregularities of the film substrate. The higher fog resistance andslipperiness can be attained by allowing the surface active agent to bepresent in the form of a band on the film surface as mentioned above.

The bleeding-out is an important factor differing in its effectdepending on the amount and the state of presence of the surface activeagent, and in the heat shrinkable film of the present invention,3.0-20.0 g/m², preferably 5.0-15.0 g/m² of the glycerin fatty acid estertype surface active agent must be present on the surface of the film. Ifthe amount of the surface active agent is less than 3.0 g/m², the filmis sometimes inferior in fog resistance and slipperiness. If it exceeds20.0 g/m², optical characteristics and slipperiness are sometimesdeteriorated for some kind of the surface active agents.

Amount (content) of the surface active agent added to the ethylenepolymer resin is 2.0-8.0% by weight, preferably 2.0-5.0% by weight basedon the total weight of the ethylene polymer resin which constitutes thefilm, taking into consideration the condition that the surface activeagent is allowed to be present in an amount of 3.0-20.0 mg/m² desirablyin the state of a band on the surface of the film.

As to whether the material distributed on the surface of the film is theglycerin fatty acid ester surface active agent or other additives, thedistribution of chemical species or functional groups on the surface ofthe film, for example, hydroxyl group and the like of the glycerin fattyacid ester surface active agent is identified by carrying out mappingwith use of analytical methods such as time-of-flight method typesecondary ion-mass spectrography (Tof-SIMS) or microscopic infraredspectroscopic analysis (ATR).

Furthermore, whether the glycerin fatty acid ester surface active agentis present in the form of a band or not can be confirmed by observingthe state of distribution of the surface active agent on the filmsurface in dynamic mode using a scanning type probe microscope such asNanoscope IIA manufactured by Digital Instruments Co., Ltd. orSPM-9500-WET-SPM series manufactured by Shimadzu Seisakusho, Ltd.

There are contact mode and dynamic mode in the measuring modes ofscanning type probe microscopes, and in the present invention,measurement is conducted in the dynamic mode. The dynamic mode is calledvibration mode or tapping mode and this mode makes it possible toobserve a soft sample which cannot be observed well in the contact mode.Specifically, whether the material present on the surface of the film isin the form of droplets or a continuous band can be simply visuallyrecognized on the image plane by observing (100-3000 magnifications) theimages of irregularities in the dynamic mode of a scanning type probemicroscope.

Detailed method of the observation will be explained later.

Thickness in the direction of band of the surface active agent band ispreferably 3-50 nm, more preferably 5-25 nm.

The thickness in the direction of band of the glycerin fatty acid estersurface active agent band is measured by catching the difference inelasticity or adsorbability (cohesive force) of the surface active agentband and the film surface by a cantilever. Specifically, first, samplesof 10 mm square are prepared from the film so as not to scratch thesurface and the whole surface of the samples is observed with amicroscope. For the observation, it is more preferred to observe samplesof several portions of the same film, for example, portions in windingdirection and width direction.

Moreover, liquid additives such as surface active agents other than theglycerin fatty acid ester surface active agents, antioxidants,antistatic agents, petroleum resins, and mineral oils may be added tothe ethylene polymer resin in such an amount as not damaging the fogresistance.

Thickness of the heat shrinkable film of the present invention ispreferably 5-30 μm, and within this range, optical characteristics andhot tack sealing strength after heat shrinking are superior. A thicknessof 8-15 μm is more preferred because optical characteristics aresuperior and, moreover, production cost is low.

Packaging speed of continuous packaging machines is conventionally about20-40 packages for 1 minute while about 60-80 packages can be finishedfor 1 minute by the recent high-speed continuous packaging machines.Therefore, heat shrinkable films are strongly demanded to haveadaptability to the packaging speed, such as slipperiness, hot tacksealability and heat shrink characteristics. For imparting thesecharacteristics to the film of the present invention, the filmpreferably has the following physical properties.

First, the heat shrinkage (shrinkage percentage) of the film will beexplained. The heat shrinkage is preferably 50-80% in both the machinedirection and the transverse direction when measured at 120° C. inaccordance with ASTM D-2732. When shrink-packaging is carried out with aheat shrinkable film having such heat shrinkage, the package can befinished tightly and beautifully. Furthermore, a beautiful packaging canbe performed with a film having a heat shrinkage in the range of 55-80%,even if the articles to be packaged are round or circular. In order toadjust the heat shrinkage of the heat shrinkable film of the presentinvention within the above range, there is a method of adjusting the gelfraction of the film to the range specified in the present invention andstretching at a high ratio (for example, 6 times or more) at atemperature higher than the melting point of the ethylene polymer resin.

Next, heat shrinkage stress of the film will be explained. The heatshrinkage stress of the heat shrinkable film of the present invention ispreferably 1.2-2.2 N/mm² in both the machine direction and thetransverse direction when measured at 120° C. in accordance with ASTMD-2838. Within this range, while the package is passed through a heatshrink tunnel, air can be easily removed from small holes, andfurthermore, since the heat shrink occurs sufficiently, creases arehardly formed. Moreover, there is no problem of deformation of thepackaged articles. More preferred range of the heat shrinkage stress is1.5-2.0 N/mm². In order for the heat shrinkage stress being in thisrange, gel fraction of the film is adjusted to the range specified inthe present invention and stretching is carried out at a high ratiowithout orientation at a temperature higher than the melting point ofthe ethylene polymer resin.

The optical characteristics of the film of the present invention will beexplained. Haze of the heat shrinkable film is measured on the filmafter heat shrunk to 30% in film area at a temperature of 140° C. inaccordance with the method of ASTM D-1003. A film of 0-3.0% in haze ispreferred because the packaged article can be easily seen through thefilm. A film having a haze of not more than 2.5% is more preferredbecause it is superior in transparency and the packaged article is seenbeautifully. In order for the haze being in this range, this can beattained by selection of catalyst used for polymerization of theethylene polymer resin, selection of comonomer, mixing of a plurality ofresins (for example, mixing a linear low density polyethylene with aspecific low density polyethylene), or adjustment of density ormolecular weight distribution of the resin and concentration of thesurface active agent.

Further, gloss of the heat shrinkable film of the present invention willbe explained. The gloss of the heat shrinkable film of the presentinvention can be obtained by carrying out the measurement on the filmafter heat shrunk to 30% in film area at a temperature of 140° C. inaccordance with the method of ASTM D-1003. A gloss of the film in therange of 130-180% is preferred. When the gloss is within this range,luster is proper to give good appearance and provide packages liked byconsumers. When the gloss of the film is 140-170%, luster increases togive high-quality feeling to the packages, and this is furtherpreferred. In order to produce a film having the gloss in the aboverange, this can be attained by selection of catalyst used forpolymerization of the ethylene polymer resin, selection of comonomer,mixing of a plurality of resins (for example, mixing a linear lowdensity polyethylene with a specific low density polyethylene), oradjustment of density or molecular weight distribution of the resin.

Furthermore, coefficient of dynamic friction of the heat shrinkable filmof the present invention will be explained. The coefficient of dynamicfriction is a property relating to slipperiness of packaging films. Thecoefficient of dynamic friction of the heat shrinkable film of thepresent invention is measured using a measuring rider of 500 g made ofmetal (satin finished surface) in accordance with ASTM D-1894. In thepresent invention, the coefficient of dynamic friction is preferably0.15-0.30. When the film has the coefficient of dynamic friction in thisrange, the film can be fed to a continuous packaging machine withoutbeing caught by the machine to cause breakage, and, besides, there areno troubles during production of the film, namely, the raw film does notslip off at a wind-up machine or the raw film does not come loose ofitself. Further, when the coefficient of dynamic friction is 0.15-0.25,the film can be suitably used in high-speed continuous packagingmachine, and this range is more preferred. In order for the coefficientof dynamic friction being in the above range, amount of the surfaceactive agent or stirring conditions may be adjusted.

Finally, hot tack sealing strength of the heat shrinkable film of thepresent invention will be explained. The hot tack sealing strength ofthe heat shrinkable film of the present invention is measured inaccordance with ASTM F-1921-98. Specifically, it is measured using HotTack measuring device manufactured by Theller Co., Ltd. at a heat sealdie temperature of 150° C. The hot tack sealing strength is preferably2.0-10.0 N. Within this range, even if heat shrinkage stress is appliedat the time of heat shrinking the film, the sealed portion is not peeleddue to this stress and occurrence of puncture can be diminished.Furthermore, there is no fear that when the sealed portion becomes hardand the hardened sealed line contacts with other packaged articles, itbreaks or scratches the film. When the hot tack sealing strength is3.0-5.0 N, the temperature in the shrink tunnel can be widely set andpassing speed can be made faster, and thus this range is more preferred.In order to obtain a film having a hot tack sealing strength in theabove range, this can be attained by selecting the kind of the ethylenepolymer resin and comonomer, mixing a plurality of resins (for example,mixing a linear low density polyethylene with a specific low densitypolyethylene), or adjusting the density or molecular weight distributionof the resin.

Method for the production of the heat shrinkable film of the presentinvention will be explained.

The heat shrinkable film can be obtained by kneading an ethylene polymerresin and a glycerin fatty acid ester surface active agent using anextruder, molding an unstretched tube, cross-linking the resultingunstretched film, and stretching the unstretched film.

As mentioned above, in the film of the present invention, the glycerinfatty acid ester surface active agent is allowed to bleed out to thesurface of the film in a high concentration, and furthermore, thesurface active agent is allowed to be present in the form of a band onthe surface of the film, whereby the amount of the surface active agenton the surface can be easily controlled and retention of fog resistanceis prolonged.

Therefore, in the method for producing the film according to the presentinvention, it is preferred that firstly the glycerin fatty acid estersurface active agent is added to the ethylene polymer resin bymaster-batch method, pouring by extruder, or the like.

Furthermore, in the present invention, it is preferred to finelydisperse the glycerin fatty acid ester surface active agent(anti-fogging agent) in the ethylene polymer resin. For this purpose, itis necessary to vigorously stir the ethylene polymer resin and theglycerin fatty acid ester surface active agent at high temperaturesusing an extruder. Specifically, in the method for the production of thefilm of the present invention, it is preferred to carry out at least apart of the kneading step of the ethylene polymer resin and the glycerinfatty acid ester surface active agent at a temperature of 250° C. orhigher and a shear rate of 50 [1/sec] or higher.

That is, the glycerin fatty acid ester surface active agent is apt toundergo heat deterioration at high temperatures, and generally thepreset temperature of the extruder is in the range of 200-240° C.However, it is necessary for finely dispersing the surface active agentin the ethylene polymer resin to carry out a part of the kneading stepat a high temperature of 250° C. or higher and a high shear rate of 50[1/sec] or higher with a short retention time, and this is acharacteristic means to allow the glycerin fatty acid ester surfaceactive agent to be present in a high concentration on the surface of thefilm.

As the extruder, either of twin-screw extruder or single screw extrudermay be used. In the case of using single screw extruder, the screw ispreferably one which can provide high kneadability, such as Dulmagescrew, cross Dulmage screw or the like. More preferred is such a screwas of a shear rate of 50 [1/sec] or higher.

For obtaining a shrinkable film having no anisotropy, for example, abiaxially stretched film of tubular type can be used. The method will beexplained.

First, a resin containing the surface active agent and others is kneadedand extruded by a ring die using a heating extruder, followed by rapidcooling with water to produce an unstretched tube.

Then, this tube is irradiated with electron rays to carry outcross-linking treatment of resin, subsequently, the tube is heated tohigher than the melting point of the resin by heat transfer heating withhot air, radiation heating with an infrared heater, or the like, andthen, while the tube is stretched in the flow direction with giving adifference in speed between two pairs of nip rolls, air is injected intothe tube thereby stretching the tube in transverse direction, too.

The stretch ratio of the heat shrinkable film of the present inventionis generally 5-10 times, preferably 5-8 times in both the machinedirection and the transverse direction for giving a high heatshrinkability to the film.

One example of a step for obtaining a shrink package using the heatshrinkable film of the present invention will be explained. The methodsfor wrapping an article with a heat shrinkable film include packagingmethods such as pillow shrink type packaging, L type packaging, and thelike. Any of them can be selected, but here the method of continuouspackaging by pillow shrink type packaging will be explained.

As articles to be packaged, there are those which are packed in plasticcontainers, such as notions and miscellaneous goods, lunches and dailydishes, and those which are packed in lidless foamed plastic trays, suchas meats, fresh fishes, Japanese-style confections, daily dishes, etc.Especially, when the containers or trays have no top lid, the heatshrinkable film is needed to have fog resistance.

First, an article is covered with a film in the tubular form which has amargin of 10-50% in length in respect to the peripheral length of thearticle in the direction perpendicular to the flow direction of thearticle, namely, in the transverse direction, and the edge portions ofthe film are superposed each other with both the portions being put flattogether in such a manner that the sealing line is positioned on thebackside of the article. The superposed portion is sealed by a centersealing apparatus of revolving roll type or the like. The sealing methodincludes impulse sealing, heat sealing, fuse sealing, or the like, andone or more of them can be selected depending on the film used. In thecase of using a high-speed continuous packaging apparatus, the heatsealing which can perform the sealing in a short time may be employed.

Subsequently, a margin of 10-50% is prepared for the length of the filmin respect to the length of the article in the flow direction of thearticle, namely, in the machine direction, and both ends of the tubularbody are sealed to close the tube and the sealed portion is cut by acutter blade. If small holes for removing air are previously made in theheat shrinkable film by needles, hot needles or laser, a tightlyfinished shrink package can be obtained by removing the air in the filmtube at the time of heat shrinking of the film.

Then, this package is passed through a hot shrink tunnel previouslyadjusted to 120° C. to obtain a finished package. If shrinking iscarried out with the hot shrink tunnel heated to higher temperatures,there are sometimes caused the troubles such as increase of haze ordeterioration of gloss of the heat shrinkable film, or breakage of thepackaging film. As a means for heating the inside of the hot shrinktunnel, hot air, vapor or the like can be used, and hot air ispreferred.

As mentioned above, since the surface active agent is present in arelatively high concentration on the surface of the heat shrinkable filmof the present invention, fog resistance and slipperiness of the filmcan be improved. Moreover, by allowing the specific surface active agentto be present in the state of a band on the surface of the film, the fogresistance and the slipperiness of the film can further be improved.

EXAMPLES

The present invention will be explained in detail by the followingexamples and comparative examples.

The evaluation methods employed in the present invention are as follows.

<Gel Fraction of Film>

A sample was subjected to extraction in boiling p-xylene for 12 hours,and the proportion of insoluble matters was expressed by the followingformula. This was used as an index of cross-linking degree of the film.

Gel fraction of film (wt %)=(weight of the sample afterextraction/weight of the sample before extraction)×100

<Density of Ethylene Polymer Resin>

This was measured in accordance with ASTM D-1505.

<Amount of Glycerin Fatty Acid Ester Surface Active Agent on the Surfaceof Film>

A sample of 1 m² was cut out from the film. The whole surface of thissample film was wiped with a fabric made of super-fine fibers (e.g.,“TORAYSEE” (registered trademark) manufactured by Toray Industries,Ltd.). As the wiping fabric, there was used a fabric previouslysubjected to Soxhlet extraction (80° C., 2 hours) to remove unnecessarymatters contained in the fabric. Operations of wiping were repeated 4-5times with changing the fabric every time. The surface active agentcontained in the fabrics after used for the wiping was extracted withchloroform, and the extraction solution was dried by an evaporator tosolidify it. Weight of the residue in the evaporator was determined bygas chromatography and this was taken as the amount of the surfaceactive agent present on the surface of the film.

<Observation of the State of Glycerin Fatty Acid Ester Surface ActiveAgent Present on the Surface of Film>

Distribution of the surface active agent in the form of a band wasobserved by a microscopic infrared spectroscopic analytical device(SPECTRA 2000 manufactured by Perkin Elmer Co., Ltd.) and a scanningtype probe microscope (NANOSCOPE III A manufactured by DigitalInstruments Co., Ltd.). The procedure was specifically as follows.

First, areas of 100 μm×100 μm of the sample were observed by themicroscopic infrared spectroscopic analytical device, and mapping of thecharacteristic peaks of the surface active agent on the surface wasconducted. Here, when there were 8 portions or more in the film wherethe band of the surface active agent was present on nearly the wholesurface of the observed image plane, it was judged that the surfaceactive agent was evenly present in the form of nearly a band on the filmsurface. This method is a simple surface observation method, andthickness of the band was measured by the method explained later.Whether the material present on the surface was surface active agent ornot was determined by confirming the presence of hydroxyl groups of thesurface active agent using a time-of-flight method type secondaryion-mass spectrography (Tof-SIMS) or a microscopic infraredspectroscopic analysis (ATR).

Subsequently, the state of presence of the surface active agent was moreexactly confirmed by the following method.

Whether the surface active agent was distributed in the form of liquiddroplets or in the form of a band on the whole surface was reconfirmedby a scanning type probe microscope. That is, a surface observation ofthe area of 10 μm×10 μm was conducted in the mode of interatomic forcemicroscopic observation. In this observation, images of 100-300magnifications were observed to confirm whether the distribution of thesurface active agent was in the form of a band or in the form ofdroplets. When droplets were present, there were seen discreteisland-like matters present in the form of dots on the image plane,while when the surface active agent was present in the form of a band,there was seen the state where mainly smooth sea continued rather thanisland-like matters.

Furthermore, thickness of the surface active agent band was measured byobtaining a force curve by scanning a given area with a cantilever ofweak spring constant (nominal value: 0.07-0.58 N/m²) in dynamic mode ofthe scanning type probe microscope. Specifically, a force curve wasprepared at randomly 50 or more points in the observation area of 10μm×10 μm and thickness of the surface active agent band was measured.For this measurement, there may also be used a scanning type probemicroscope which can perform mapping.

<Evaluation of Heat Shrinkage>

This was measured in accordance with ASTM D-2732 by carrying outshrinking at a temperature of 120° C. The following evaluation wasconducted on shrinkage percentage.

[Criteria of Evaluation]

-   -   ⊚: Not less than 55% and less than 80%. A beautiful shrink        package was obtained and this was particularly preferred.    -   ◯: Not less than 50% and less than 55%. A shrink package was        obtained and this was preferred.    -   Δ: Not less than 30% and less than 50%. Fine creases occurred,        and the film could hardly be used.    -   x: Less than 30%, and the film could not be used.        <Evaluation of Heat Shrinkage Stress>

A maximum heat shrinkage stress at a temperature of 120° C. was measuredin accordance with ASTM D-2838.

[Criteria of Evaluation]

-   -   ⊚: Not less than 1.5 N/mm² and less than 2.0 N/mm². A beautiful        shrink package was obtained without causing deformation of the        article packaged.    -   ◯: Not less than 1.2 N/mm² and less than 1.5 N/mm², or more than        2.0 N/mm² and less than 2.2 N/mm². A shrink package could be        obtained without causing deformation of the article packaged.    -   Δ: Not less than 0.8 N/mm² and less than 1.2 N/mm², or more than        2.2 N/mm² and less than 2.5 N/mm². The film could hardly be        used.    -   x: Less than 0.8 N/mm² or more than 2.5 N/mm². The film was        practically not acceptable.        <Evaluation of Haze>

Evaluation was conducted by measuring a haze of the film when it washeat shrunk to 30% in area at a temperature of 140° C., in accordancewith a method of ASTM D-1003.

[Criteria of Evaluation]

-   -   ⊚: Not more than 2.5%. The package had no haze and was        beautifully finished.    -   ◯: More than 2.5% and not more than 3%. The package had some        haze, but was beautifully finished.    -   Δ: More than 3% and not more than 5%. The package had haze and        the film could hardly be used.    -   x: More than 5%. The package appeared whitish and the film could        not be practically used.        <Evaluation of Gloss>

Evaluation was conducted by measuring a gloss of the film at an angle of45° which was heat shrunk to 30% in area at a temperature of 140° C., inaccordance with a method of ASTM D-1003.

[Criteria of Evaluation]

-   -   ⊚: Not less than 140% and not more than 180%. The film showed        high-grade appearance.    -   ◯: Not less than 130% and less than 140%. The film had a proper        gloss and gave a beautiful package.    -   Δ: Not less than 110% and less than 130%. The film was        insufficient in gloss and the film could hardly be used.    -   x: Less than 110%. The film was insufficient in gloss, and could        not be practically used.        <Evaluation of Slipperiness>

This was evaluated by coefficient of dynamic friction measured using arider of 500 g made of metal (satin finished surface) in accordance withASTM D-1894.

[Criteria of Evaluation]

-   -   ⊚: Not less than 0.15 and not more than 0.25. The film was        sufficient for practical use.    -   ◯: More than 0.25 and not more than 0.30. The film was        practically acceptable.    -   Δ: Less than 0.15 or more than 0.30 and not more than 0.35. The        film could hardly be used.    -   x: More than 0.35. There was the possibility of the film being        frequently broken, and could not be practically used.        <Evaluation of Hot Tack Sealing Strength>

This was measured in accordance with ASTM F-1921-98 using a Hot Tackmeasuring device manufactured by Theller Co., Ltd. The film was sealedto a test piece of 25 mm in width at a temperature of 150° C. using aV-shaped heat sealing die. Peeling was carried out, and the hot tacksealing strength which changed with time was plotted on the order of1/1000 seconds, and evaluation was conducted by measuring a sealingstrength after 0.25 second from the starting of peeling.

[Criteria of Evaluation]

-   -   ⊚: Not less than 3.0 and not more than 5.0. This was practically        very preferable level.    -   ◯: Not less than 2.0 N and less than 3.0 or more than 5.0 N and        not more than 10.0 N. This was a practically acceptable level.    -   Δ: Not less than 1.6 N and less than 2.0 N. Peeling of seal        sometimes occurred and use of the film was difficult.    -   x: Less than 1.6 N. Peeling of seal frequently occurred, and the        film was practically not acceptable.        <Evaluation of Fog Resistance>

Evaluation of fog resistance was conducted in the following manner.Water adjusted to 20° C. was charged in a beaker of 500 ml, and thebeaker was closed by covering the top with a film. This beaker wasstored in a refrigerated counter adjusted to 10° C., and the fogresistance was evaluated by grading the state of water droplets attachedto the film and the visibility through the film after lapse of 30minutes and indicated by 1-5 marks with 5 marks being perfect.

[Criteria of Evaluation]

-   -   ⊚: 5 marks: There were no spots of water droplets and visibility        is satisfactory, and the film was practically acceptable.    -   ◯: 4 marks: There were some large water droplets, but visibility        was good, and the film was practically acceptable.    -   Δ: 2-3 marks: There were considerable small water droplets and        visibility was inferior, and the film was could hardly be used.    -   x: 1 mark: The film was fogged with many small water droplets        and visibility was seriously bad, and the film was practically        not acceptable.        <Overall Evaluation>    -   ⊚: All evaluations were ⊚ and the film could be suitably used as        a heat shrinkable film.    -   ◯: All evaluations were ◯ or ⊚ and the film could be practically        used as a heat shrinkable film.    -   Δ: The evaluations included Δ and the film could hardly be used        as a heat shrinkable film.    -   x: The evaluations included x and the film was practically not        acceptable.

Examples 1-24

Films were prepared using the ethylene polymer resins and theglycerin-based surface active agents shown in Table 1 for Examples 1-24.In Table 1, “SSC” means that the polymers were obtained usingsingle-site catalysts and “MSC” means that the polymers were obtainedusing multi-site catalysts (the same shall apply to Table 2). In thecase of producing a film of 3 layer structure comprising two outerlayers and an inner layer comprising 2 kinds of the resins, twoextruders and ring dies were used, and in the case of producing a filmof single layer, one extruder was used. A tube was melt extruded fromthe ring die, and the tube was rapidly cooled using a water-cooled ring.Unstretched tubes of about 500 μm thick were obtained by the abovemethods.

The ratio of the layers of the two outer layers and the inner layer inthe three layer film was such that the outer layers were 15% and 15%,and 30% in total, and the inner layer was 70%. The surface active agentwas added to the ethylene polymer resin by a master batch method. Thatis, the surface active agent and a part of the ethylene polymer resinwere kneaded by a twin-screw extruder to make a master batch, and thiswas added to the remaining ethylene polymer resin.

As the extruder for the molding of unstretched tube, a single screwextruder was used, and a Dulmage screw was used as the screw. Thestirring shear force of the screw was all 100 [1/sec]. Temperature ofthe extruder was set at 200° C., 230° C., 250° C., 260° C., 260° C. and260° C. in order from the resin feeding hopper side at six temperaturecontrolling blocks in longer direction. The shear rate was a rategradient from shear moving rate (moving rate by revolution of screw) atthe cylinder wall surface, assuming the rate at the screw wall surfaceto be 0, and this was obtained by simulating as a drag flow (averagevalue).

The resulting unstretched tube was irradiated with 4 megarads ofelectron rays accelerated with an accelerating voltage of 500 kV,thereby cross-linking the tube. Subsequently, the unstretched tube wasstretched to 7 times in flow direction by the difference in speedbetween two pairs of nip rolls while being heated to 140° C. byradiation heating with an infrared heater. Then, air was injected intothe tube to stretch the tube in the direction perpendicular to the flowdirection of the machine. Thereafter, the portion of the maximumdiameter of the bubble was exposed to a cold air by an air ring to coolthe bubble. The resulting film was then folded to obtain raw films forpackaging films of Examples 1-24 which had a thickness of about 10 μm.

The heat shrinkable raw films were stored in a room adjusted to atemperature of 40° C. for 3 days, and then the state of the glycerinfatty acid ester surface active agent present on the surface of the filmwas observed in the manner mentioned above to confirm whether it waspresent in the form of a band or not. The unit of “thicknessdistribution” in Tables 1-2 is “nm”.

Then, these heat shrinkable films were evaluated on the above-mentionedheat shrinkage, heat shrinkage stress, haze, gloss, slipperiness, hottack sealing strength, and fog resistance, and overall evaluation ofthem was conducted. The results are shown in Table 3.

As a result, it was seen that the resulting heat shrinkable films werevery good in both the slipperiness and haze, and when the glycerin fattyacid ester surface active agent was present in an amount of 3.0-20.0mg/m² and in the form of a band on the surface, the fog resistance wasstable and superior. Furthermore, these films were low in heat shrinkagestress while they were high in shrinking performance, and besides theywere markedly excellent in transparency and gloss after shrinking.

Moreover, it was seen from the results of Examples 11, 17 and 18 thatthe heat shrinkage stress varied depending on the irradiation dose (gelfraction of the film), and there was a tendency of increase of heatshrinkage stress with increase of the gel fraction of the film.

It was also seen from the results of Examples 2, 10, 11 and 15 that theslipperiness, optical characteristics and sealability varied dependingon the kind of the ethylene copolymer resin used.

Further, the films of Examples 1-12, 14, 16-18 and 21-24 were very goodin extrusion stability and stretching stability, and unevenness inthickness of the films was very small.

Comparative Examples 1-8

Films were obtained in the same manner as in Example 1, except thatcomposition of the resin in each layer was changed as shown in Table 2,and after the addition of the surface active agent, kneading was carriedout at 230° C. by a single flight screw (shear rate: 40 [1/sec]). InComparative Examples 7-8, the surface active agent was further coated onthe surface so that the amount of the surface active agent on thesurface (amount of the surface active agent which bled to the surface +amount of the coated surface active agent) was 3.0 mg/m². These wereComparative Examples 1-8, and the results are shown in Table 4.

According to Table 4, as can be seen from the results of ComparativeExample 1, when the film was stretched at a high temperature with anirradiation dose of less than 2 megarads (1 megarad, gel fraction 4%),the heat shrinkable film was low in heat shrinkage stress.

Conversely, as can be seen from the results of Comparative Example 2,when the irradiation dose was higher than 10 megarads (12 megarads, gelfraction 45%), there was obtained a packaging film which was too high inheat shrinkage stress.

On the other hand, as can be seen from the results of ComparativeExamples 3-6, even if the glycerin fatty acid ester surface active agentwas distributed in the form of a band, a sufficient fog resistance couldnot be obtained if the amount thereof on the surface was less than 3.0mg/m². Furthermore, even if the amount thereof on the surface was notless than 3.0 mg/m², no satisfactory fog resistance could be obtained ifthe surface active agent was present in the form of dots.

TABLE 1 Ex. Composition of ethylene polymer resin Surface active agent 1Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt %Diglycerin oleate Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926MI=2.0 30 wt % Low density polyethylene ρ=0.920 MI=0.4 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture ofdiglycerin 2 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 30 wt % oleate and glycerin Inner layer: Ethylene-α-olefin(octene-1) MSC ρ=0.926 MI=2.0 monooleate (1:1) Low density polyethyleneρ=0.920 MI=0.4 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 3 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70wt % Mixture of diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSCρ=0.926 MI=2.0 30 wt % oleate and glycerin Low density polyethyleneρ=0.920 MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 4 Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture of diglycerin Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % oleate andglycerin Low density polyethylene ρ=0.920 MI=0.4 monooleate (1:1) Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 5 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture ofdiglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.030 wt % oleate and glycerin Low density polyethylene ρ=0.920 MI=0.4monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 6 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70wt % Mixture of diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSCρ=0.926 MI=2.0 30 wt % oleate and glycerin Low density polyethyleneρ=0.920 MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 7 Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Diglycerin laurate Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % Low densitypolyethylene ρ=0.920 MI=0.4 Outer layer: Ethylene-α-olefin (hexene-1)SSC ρ=0.914 MI=2.0 8 Outer layer: Ethylene-α-olefin (hexene-1) SSCρ=0.914 MI=2.0 70 wt % Glycerin monooleate Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % Low densitypolyethylene ρ=0.920 MI=0.4 Outer layer: Ethylene-α-olefin (hexene-1)SSC ρ=0.914 MI=2.0 Amount of surface Amount on the Surface distributionIrradiation active agent added surface (thickness distribution) (gelfraction) 2.5 wt % 3.0 mg/m² band 4 (5-20) (20%) 2.5 wt % 3.0 mg/m² band4 (5-20) (20%) 2.5 wt % 4.0 mg/m² band 4 (5-30) (20%) 2.5 wt % 5.0 mg/m²band 4 (5-40) (20%) 2.0 wt % 3.0 mg/m² band 4 (5-40) (20%) 3.0 wt % 5.0mg/m² band 4 (5-40) (20%) 3.0 wt % 5.0 mg/m² band 4 (5-40) (20%) 3.0 wt% 5.0 mg/m² band 4 (5-20) (20%) Ex. Composition of ethylene polymerresin Surface active agent 9 Outer layer: Ethylene-α-olefin (octene-1)MSC ρ=0.914 MI=1.0 70 wt % Diglycerin oleate Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % Low densitypolyethylene ρ=0.920 MI=0.4 Outer layer: Ethylene-α-olefin (octene-1)MSC ρ=0.914 MI=1.0 10 Outer layer: Ethylene-α-olefin (octene-1) MSCρ=0.914 MI=1.0 70 wt % Mixture of diglycerin Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % oleate andglycerin Low density polyethylene monooleate (1:1) Outer layer:Ethylene-α-olefin (octene-1) MSC ρ=0.914 MI=1.0 11 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixture ofdiglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 70wt % monooleate (1:1) Low density polyethylene ρ=0.920 MI=0.4 30 wt %Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Lowdensity polyethylene ρ=0.922 MI=0.5 10 wt % 12 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixture ofdiglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 70wt % monooleate (1:1) Low density polyethylene ρ=0.920 MI=0.4 30 wt %Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Lowdensity polyethylene ρ=0.922 MI=0.5 10 wt % 13 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixture ofdiglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.919 MI=2.0monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Low density polyethylene ρ=0.922 MI=0.5 10 wt % 14 Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixtureof diglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.925 MI=2.0monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Low density polyethylene ρ=0.922 MI=0.5 10 wt % 15 Singlelayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixtureof diglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Amount of surface Amount on the Surface distributionIrradiation active agent added surface (thickness distribution) (gelfraction) 2.5 wt % 3.0 mg/m² band 4 (5-20) (20%) 2.5 wt % 3.0 mg/m² band4 (5-20) (20%) 2.5 wt % 4.0 mg/m² band 4 (5-35) (20%) 3.0 wt % 5.0 mg/m²band 4 (5-40) (20%) 3.0 wt % 4.0 mg/m² band 4 (5-30) (20%) 3.0 wt % 4.0mg/m² band 4 (5-30) (20%) 2.5 wt % 3.0 mg/m² band 4 (5-20) (20%) Ex.Composition of ethylene polymer resin Surface active agent 16 Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixtureof diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926MI=2.0 30 wt % oleate and glycerin Low density polyethylene ρ=0.920MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSCρ=0.914 MI=1.0 17 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Mixture of diglycerin Low density polyethylene ρ=0.922MI=0.5 10 wt % oleate and glycerin Inner layer: Ethylene-α-olefin(octene-1) MSC ρ=0.926 MI=2.0 70 wt % monooleate (1:1) Low densitypolyethylene ρ=0.920 MI=0.4 30 wt % Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Low density polyethylene ρ=0.922MI=0.5 10 wt % 18 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Mixture of diglycerin Low density polyethylene ρ=0.922MI=0.5 10 wt % oleate and glycerin Inner layer: Ethylene-α-olefin(octene-1) MSC ρ=0.926 MI=2.0 70 wt % monooleate (1:1) Low densitypolyethylene ρ=0.920 MI=0.4 30 wt % Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Low density polyethylene ρ=0.922MI=0.5 10 wt % 19 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Mixture of diglycerin Low density polyethylene ρ=0.922MI=0.5 10 wt % oleate and glycerin Inner layer: Ethylene-α-olefin(octene-1) MSC ρ=0.926 MI=2.0 70 wt % monooleate (1:1) Low densitypolyethylene ρ=0.920 MI=0.4 30 wt % Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Low density polyethylene ρ=0.922MI=0.5 10 wt % 20 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 90 wt % Mixture of diglycerin Low density polyethylene ρ=0.922MI=0.5 10 wt % oleate and glycerin Inner layer: Ethylene-α-olefin(octene-1) MSC ρ=0.926 MI=2.0 70 wt % monooleate (1:1) Low densitypolyethylene ρ=0.920 MI=0.4 30 wt % Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Low density polyethylene ρ=0.922MI=0.5 10 wt % Amount of surface Amount on the Surface distributionIrradiation active agent added surface (thickness distribution) (gelfraction) 2.5 wt % 4.0 mg/m² band 2 (5-30) (10%) 2.5 wt % 4.0 mg/m² band2 (5-30) (10%) 2.5 wt % 4.0 mg/m² band 8 (5-30) (30%) 5.0 wt % 14.0mg/m² band 4 (5-45) (20%) 8.0 wt % 20.0 mg/m² band 4 (5-50) (20%) Ex.Composition of ethylene polymer resin Surface active agent 21 Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixtureof diglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.925 MI=2.0 70wt % monooleate (1:1) Low density polyethylene ρ=0.920 MI=0.2 30 wt %Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Lowdensity polyethylene ρ=0.922 MI=0.5 10 wt % 22 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixture ofdiglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.926 MI=2.0 60wt % monooleate (1:1) Low density polyethylene ρ=0.920 MI=0.2 40 wt %Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Lowdensity polyethylene ρ=0.922 MI=0.5 10 wt % 23 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Mixture ofdiglycerin Low density polyethylene ρ=0.922 MI=0.5 10 wt % oleate andglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.913 MI=3.0 65wt % monooleate (1:1) Low density polyethylene ρ=0.922 MI=0.4 35 wt %Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 90 wt % Lowdensity polyethylene ρ=0.922 MI=0.5 10 wt % 24 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 65 wt % Mixture ofdiglycerin Inner layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.925 MI=2.035 wt % oleate and glycerin Low density polyethylene ρ=0.920 MI=0.2monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 Amount of surface Amount on the Surface distribution Irradiationactive agent added surface (thickness distribution) (gel fraction) 3.0wt % 4.0 mg/m² band 4 (5-30) (20%) 3.0 wt % 4.0 mg/m² band 4 (5-30)(20%) 3.0 wt % 4.0 mg/m² band 4 (5-30) (20%) 3.0 wt % 4.0 mg/m² band 4(5-30) (20%)

TABLE 2 Comp. Ex. Composition of ethylene polymer resin Surface activeagent 1 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.890 MI=2.0 70wt % Mixture of diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSCρ=0.926 MI=2.0 30 wt % oleate and glycerin Low density polyethyleneρ=0.920 MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.890 MI=2.0 70 wt % Mixture of diglycerin 2 Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.937 MI=2.0 30 wt % oleateand glycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926MI=2.0 monooleate (1:1) Low density polyethylene ρ=0.920 MI=0.4 Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.937 MI=2.0 3 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture ofdiglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.030 wt % oleate and glycerin Low density polyethylene ρ=0.920 MI=0.4monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 4 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70wt % Mixture of diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSCρ=0.926 MI=2.0 30 wt % oleate and glycerin Low density polyethyleneρ=0.920 MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 5 Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture of diglycerin Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % oleate andglycerin Low density polyethylene ρ=0.920 MI=0.4 monooleate (1:1) Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 6 Outer layer:Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture ofdiglycerin Inner layer: Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.030 wt % oleate and glycerin Low density polyethylene ρ=0.920 MI=0.4monooleate (1:1) Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914MI=2.0 7 Outer layer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 70wt % Mixture of diglycerin Inner layer: Ethylene-α-olefin (octene-1) MSCρ=0.926 MI=2.0 30 wt % oleate and glycerin Low density polyethyleneρ=0.920 MI=0.4 monooleate (1:1) Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 8 Outer layer: Ethylene-α-olefin(hexene-1) SSC ρ=0.914 MI=2.0 70 wt % Mixture of diglycerin Inner layer:Ethylene-α-olefin (octene-1) MSC ρ=0.926 MI=2.0 30 wt % oleate andglycerin Low density polyethylene ρ=0.920 MI=0.4 monooleate (1:1) Outerlayer: Ethylene-α-olefin (hexene-1) SSC ρ=0.914 MI=2.0 Amount of surfaceAmount on the Surface distribution Irradiation active agent addedsurface (thickness distribution) (gel fraction) 2.5 wt % 3.0 mg/m² band4 (5-10) (20%) 2.5 wt % 3.0 mg/m² band 4 (5-10) (20%) 2.5 wt % 3.0 mg/m²band 1 (5-10) (4%) 2.5 wt % 3.0 mg/m² band 12 (5-20) (45%) 1.5 wt % 1.5mg/m² band 4 (5-10) (20%) 2.0 wt % 1.5 mg/m² band 4 (5-10) (20%) 0.5 wt% 3.0 mg/m² band 4 (Coating) (0-300) (20%) 1.5 wt % 3.0 mg/m² band 4(Coating) (0-550) (20%)

TABLE 3 Evaluation Example Example Example Example Example ExampleExample Example Example Example items 1 2 3 4 5 6 7 8 9 10 Heatshrinkage 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56⊚ 57/56 ⊚ 57/56 ⊚ (%) MD/TD Heat shrinkage 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.8 ⊚ 1.8/1.8 ⊚stress (N/mm²) MD/TD Haze after 2.3 ⊚ 2.4 ⊚ 2.3 ⊚ 2.3 ⊚ 2.4 ⊚ 2.3 ⊚ 3.0◯ 3.0 ◯ 2.2 ⊚ 2.2 ⊚ shrinking (%) Gloss after 145 ⊚ 145 ⊚ 145 ⊚ 146 ⊚145 ⊚ 146 ⊚ 139 ◯ 139 ◯ 150 ⊚ 150 ⊚ shrinking (%) Shipperness 0.22 ⊚0.21 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.21 ⊚ 0.30 ◯ 0.30 ◯(coefficient of dynamic friction) Hot tack 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 4.0 ⊚4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 3.0 ⊚ 3.0 ⊚ sealing strength (N) Fog 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ 5⊚ 5 ⊚ 5 ⊚ 4 ◯ 5 ⊚ 5 ⊚ resistance Overall ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ◯ ◯ ◯ EvaluationEvaluation Example Example Example Example Example Example ExampleExample Example Example items 11 12 13 14 15 16 17 18 19 20 Heatshrinkage 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/56 ⊚ 57/57 ⊚ 53/52 ◯ 53/52 ◯ 59/58⊚ 57/56 ⊚ 57/56 ⊚ (%) MD/TD Heat shrinkage 1.8/1.8 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚1.8/1.7 ⊚ 1.8/1.8 ⊚ 1.5/1.4 ◯ 1.5/1.4 ◯ 2.2/2.1 ◯ 1.8/1.8 ⊚ 1.8/1.8 ⊚stress (N/mm²) MD/TD Haze after 2.3 ⊚ 2.2 ⊚ 2.2 ⊚ 2.2 ⊚ 2.3 ⊚ 2.3 ⊚ 2.3⊚ 2.3 ⊚ 1.8 ⊚ 2.3 ⊚ shrinking (%) Gloss after 145 ⊚ 150 ⊚ 150 ⊚ 150 ⊚145 ⊚ 145 ⊚ 145 ⊚ 145 ⊚ 152 ⊚ 145 ⊚ shrinking (%) Shipperness 0.23 ⊚0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.25 ⊚ 0.29 ◯(coefficient of dynamic friction) Hot tack 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 4.0 ⊚4.0 ⊚ 4.0 ⊚ 2.0 ◯ 4.0 ⊚ 4.0 ⊚ sealing strength (N) Fog 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ 4◯ 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ resistance Overall ⊚ ⊚ ⊚ ⊚ ◯ ◯ ◯ ◯ ⊚ ◯ EvaluationEvaluation Example Example Example Example items 21 22 23 24 Heatshrinkage 57/56 ⊚ 56/56 ⊚ 56/56 ⊚ 57/56 ⊚ (%) MD/TD Heat shrinkage1.8/1.8 ⊚ 1.7/1.7 ⊚ 1.8/1.8 ⊚ 1.8/1.7 ⊚ stress (N/mm²) MD/TD Haze after2.1 ⊚ 2.3 ⊚ 2.0 ⊚ 2.2 ⊚ shrinking (%) Gloss after 149 ⊚ 148 ⊚ 150 ⊚ 145⊚ shrinking (%) Shipperness 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.23 ⊚ (coefficient ofdynamic friction) Hot tack 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ 4.0 ⊚ sealing strength (N)Fog 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ resistance Overall ⊚ ⊚ ⊚ ⊚ Evaluation

TABLE 4 Compara- Compara- Compara- Compara- Compara- Compara- Compara-Compara- tive tive tive tive tive tive tive tive Evaluation ExampleExample Example Example Example Example Example Example items 1 2 3 4 56 7 8 Heat shrinkage 53/50 ◯ 59/58 ⊚ 50/50 ◯ 59/58 ⊚ 57/56 ⊚ 57/56 ⊚57/56 ⊚ 57/56 ⊚ (%) MD/TD Heat shrinkage 1.4/1.4 ◯ 2.2/2.1 ◯ 1.2/1.1 Δ2.4/2.3 Δ 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚ 1.8/1.7 ⊚ stress (N/mm²) MD/TDHaze after 2.5 ⊚ 4.5 Δ 2.6 ◯ 2.6 ◯ 2.5 ⊚ 2.5 ⊚ 2.5 ⊚ 2.5 ⊚ shrinking (%)Gloss after 140 ⊚ 120 Δ 138 ◯ 140 ⊚ 145 ⊚ 145 ⊚ 145 ⊚ 145 ⊚ shrinking(%) Shipperness 0.36 x 0.22 ⊚ 0.22 ⊚ 0.22 ⊚ 0.21 ⊚ 0.21 ⊚ 0.21 ⊚ 0.21 ⊚(coefficient of dynamic friction) Hot tack 1.0 x 1.0 x 4.5 ⊚ 1.8 Δ 4.0 ⊚4.0 ⊚ 4.0 ⊚ 4.0 ⊚ sealing strength (N) Fog 5 ⊚ 5 ⊚ 5 ⊚ 5 ⊚ 2 Δ 2 Δ 2 Δ 2Δ resistance Overall x x Δ Δ Δ Δ Δ Δ Evaluation

INDUSTRIAL APPLICABILITY

The heat shrinkable films of the present invention are not high inshrinkage stress while being high in shrink performance, and areexcellent in transparency and gloss even after being shrunk, and hence,they can be preferably used for shrink package. Moreover, they can besuitably used for uses requiring fog resistance.

Furthermore, since the heat shrinkable films of the present inventionare good in slipperiness and high in hot tack sealing strength, they canalso be used as packaging films applicable to high-speed continuouspackaging machines.

1. A cross-linked heat shrinkable laminate film where the laminate filmcomprises at least 3 layers composed of outer layers and an inner layer,two outer layers and an inner layer comprise an ethylene polymer resinhaving a density of 0.900-0.934 g/cm³, and said ethylene polymer resinis at least one member selected from the group consisting of (i)intermediate density polyethylene; (ii) low density polyethylene; (iii)ethylene-α-olefin copolymer comprising linear low density polyethyleneand/or ultra-low density polyethylene; and (iv) mixtures thereof, andthe outer layers comprise one member selected from the group consistingof an ethylene-α-olefin copolymer, a low density polyethylene andmixtures thereof, the laminate film has a gel fraction of 5-40% andcontains a glycerin fatty acid ester surface active agent in an amountof 2.0-8.0% by weight based on the total weight of the ethylene polymerresin, and said surface active agent is present in an amount of 3.0-20.0mg/m² on at least one surface of the film, and the heat shrinkage of thefilm at 120° C. is 50-80% in both the machine direction and thetransverse direction and the transverse direction, and the heatshrinkage stress of the film at 120° C. is 1.2-2.2 N/mm² in both themachine direction and the transverse direction.
 2. A heat shrinkablefilm according to claim 1, wherein the haze of the film which is heatshrunk to 30% in film area at 140° C. is 0-3.0% and the gloss of thefilm which is heat shrunk to 30% in film area at 140° C. is 130-180%. 3.A heat shrinkable film according to claim 1, wherein the coefficient ofdynamic friction of the film is 0.15-0.30 and the hot tack sealingstrength of the film when temperature of heat sealing die is 150° C. is2.0-10.0 N.
 4. A heat shrinkable film according to claim 1 which has athickness of 5-30 μm.
 5. A heat shrinkable film according to claim 1which is a laminate film comprising three layers of outer layers and aninner layer, the outer layers and/or the inner layer being layerscontaining an ethylene-α-olefin copolymer obtained using a single-sitecatalyst.
 6. A method for producing a heat shrinkable film including thesteps of kneading an ethylene polymer resin having a density of0.900-0.934 g/cm ³ and a glycerin fatty acid ester surface active agentusing an extruder, molding an unstretched tube, cross-linking theresulting unstretched tube, and stretching the tube, wherein at least apart of the kneading step is carried out at a temperature of not lowerthan 250° C. and at a shear rate of not less than 50 [1/sec], thestretching step is carried out at a temperature higher than the meltingpoint of the resin, and said ethylene polymer resin is at least onemember selected from the group consisting of (i) intermediate densitypolyethylene; (ii) low density polyethylene; (iii) ethylene-α-olefincopolymer comprising linear low density polyethylene and/or ultra-lowdensity polyethylene; and (iv) mixtures thereof.
 7. A heat shrinkablefilm obtained by the method according to claim 6.